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Medium Voltage Dry Type Substation Transformers
Sales Guide
(323) 726-0888 • (800) 423-4366 • www.mgmtransformer.com
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Table of Contents
Company Profile ................................................................................................................................ 3
How to Sell Medium Voltage Transformers ......................................................................................... 4
Vacuum Pressure Impregnated (VPI) Specification Guide .................................................................... 5
Medium Voltage Transformer Parts .................................................................................................... 9
Glossary of Terms ............................................................................................................................ 10
Take Off Sheet ................................................................................................................................. 11
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Company Profile
For over four decades, MGM Transformer Company has been a reliable source for quality
substation transformers. Our abilities cover the full range of requirements from 600v to 34.5kV,
500kVA to 10,000kVA. As an engineering-oriented transformer company, we maintain a large
in-house engineering staff at both our factories. Our experience in working with various
switchgear manufacturers enables us to design the high voltage/low voltage switchgear
interface, assuring the proper match in the field. Flex connectors can also be supplied. Non-
standard substation designs are also available for special situations such as failed unit
retrofitting or PCB replacements. All manufacturing processes are done on the premises. This
advantage, along with a large inventory of electrical steel and wire, assures our customers the
industry’s shortest standard lead times, regardless of the interface
requirements.
General Construction
Coils are vacuum pressure impregnated (VPI) with sol ventless polyester resin, ensuring
complete impregnation of the windings and insulation. The finished VPI coils are incredibly
strong, readily dissipate heat and are protected against moisture, dirt and most industrial
contaminants. Ventilated dry-type winding designs vary depending on the voltage, basic
impulse level (BIL) and current of the individual winding and/or application of the transformer.
For all units, the insulation system will be 220°C regardless of the average winding rise.
MGM ventilated dry-type transformers are designed for indoor or outdoor applications in
schools, hospitals, industrial plants, commercial buildings and any place requiring safe and
dependable power. Ventilated dry-type transformers offer an economical solution and are
extremely reliable when properly installed and maintained.
Bull Rush Program
Need it fast? We can deliver. Emergencies happen and we can expedite the manufacturing of
your units to meet your delivery requirements. Ask about our Bull Rush program when you
place your order and we can manufacture and ship your unit in as fast as 5 working days!
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How do I sell Medium Voltage (MV) Transformers?
You start with a Fast/Accurate MV Transformer Quote
WHEN YOU GET AN INVITATION TO QUOTE ON MEDIUM VOLTAGE DRY TRANSFORMER, WHAT DO YOU DO?
1. Send the inquiry immediately to your assigned MGM SAE for a quotation that you can
present back to your customer?
2. Give thought about what will be required for you to book the order?
3. What will be your course of action?
a. Get a “feel” for pricing and delivery needed. (Don’t rely on standard lead times)
b. Be sure that MGM is approved.
c. Why is the customer asking for a quote? Budgetary, Bid, or Buy?
d. Get information on your competition:
• Is Liquid Filled in the picture?
• Will the customer consider a “Used” or “Repaired” transformer?
• Will a switchgear manufacturer try to “package” you out?
• Does the customer know all the MGM Transformer advantages?
e. Get a complete understanding of all the ratings, features, and other associated
equipment that will be purchased along with the purchase of the transformer. Will
the customer need to buy a PLI (aka primary load interrupter)
f. Know who will really make the final buying decision and what criteria will be used
in making this decision. How do you propose to influence this decision maker to
buy our equipment?
**Included as part of this newsletter is the Specification Guide and the Transformer Specification
Checklist. The Specification Guide will be available in Word for engineers to use to specify MGM
transformers.
Accompanying the Specification Guide is the Transformer Specification Checklist, which contains
the basic information needed to offer an accurate and successful proposal. In this checklist you
will see places to indicate the winding material, winding temperature rise, BIL, indoor or outdoor,
the method of connecting the transformer to other equipment, and the “ship to” destination. All
the items in this checklist are important for us to know so we can offer the best proposal for
success.
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Vacuum Pressure Impregnated (VPI)
Dry-Type Substation Transformer
Specification Guide
This specification provides technical requirements for the design, manufacture, and testing of
substation transformers.
This specification covers only the general requirements of the transformer. The specific
requirements will be given in detail on the attached Transformer Data Sheet.
Transformer Technical Requirements
Description
Dry type vacuum pressure impregnated construction, mounted in a suitably ventilated
enclosure.
Primary and secondary voltages shall be as indicated on the data sheet
Core Characteristics
The transformer core shall be constructed of high grade non-aging silicon steel laminations with
high magnetic permeability and low hysteresis and eddy current losses. Magnetic flux densities
are to be kept well below the saturation point. A step lap mitered core joint shall be used to
minimize losses, exciting currents and sound levels. The core laminations shall be clamped
together with heavy steel members.
Temperature Rise
The average temperature rise of the transformer windings shall be rated at (80°C, 115°C, 150°C)
and shall be built utilizing Class 220°C insulations, regardless of the temperature rise specified.
The transformer shall not exceed the specified temperature rise when the unit is operated
continuously at full nameplate rating. The transformer shall be capable of carrying 100% of the
nameplate rating in a 40°C maximum, 30°C 24 hour period average ambient.
Coil Characteristics
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The high voltage and low voltage windings shall be constructed using copper or aluminum
conductors as indicated on the data sheet. The conductors shall be insulated with a 220°C
insulation. .
The high voltage winding shall be wound over the low voltage winding with sufficient
mechanical bracing to prevent movement during fault conditions and sufficient solid Class
220°C insulation to isolate the high voltage winding dielectric potential from the low voltage
windings.
Taps
Transformer primary winding shall have adjustable taps as indicated on the data sheet. Taps
shall be for de-energized operation only.
Vacuum Pressure Impregnation Process
The coils shall be dried at atmospheric pressure in an oven through which hot air is
continuously circulated. The totally dried coils shall be vacuum pressure impregnated in
polyester resin varnish.
The VPI process shall apply a one (1) cycle polyester protective shield of varnish to the coils. The
VPI process shall effectively impregnate the coil assemblies, thus resulting in a unit which is
virtually impermeable to moisture, dust, dirt, salt air, and other industrial contaminants. The
VPI processed coils shall be permanently assembled on the core, and then dipped in polyester
resin varnish. The varnish shall be cured on the core and coil assembly following an established
temperature vs. time baking cycle in a hot air circulating oven.
Core and Coil Assembly
After installation of windings on core and stacking of the top yoke core steel, core and coil
assembly is to be secured with a rigid frame. Primary and secondary coordination bus
assemblies, as required for connection to associated switchgear are to be of welded or bolted
construction.
Dielectric Threshold
The impulse rating of the transformer must equal or exceed the basic impulse level specified by
ANSI for the applicable voltage class. The basic impulse level shall be inherent to the winding
design and is to be obtained without the use of supplemental surge arrestors.
Vibration Isolation
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The transformer shall have vibration isolation pads installed between core and coil assembly
and enclosure base structures to prevent the transmission of structure borne vibration. The
pads shall be neoprene-cork-neoprene sandwich type.
Enclosure
The enclosure shall be constructed of heavy gauge sheet steel and shall be finished in ANSI 61
paint color applied using either a powder coat paint system. All ventilating openings shall be in
accordance with NEMA and NEC standards for ventilated enclosures. The base of the enclosure
shall be furnished with ground pads located on opposite diagonal corners. The base shall have
jacking pads and shall be constructed of heavy steel members to permit skidding or rolling in
any direction.
Optional – Transformer case anchoring provisions shall be certified to meet California Building
Code (CBC) Zone 4 seismic requirements with seismic table validation.
Optional - OSHPD certification is also available.
Optional – Enclosures can be constructed to provide NEMA 3R protection against rain, sleet and
external ice construction.
Nameplate
Transformer shall be furnished with a non-corrosive diagrammatic nameplate per ANSI
C57.12.01, permanently attached with non-corrosive hardware. The diagrammatic nameplate
shall include the name of the manufacturer of the transformer as well as the location where the
transformer was manufactured and tested
Forced Air Cooling
Forced air cooling, when required, shall increase the continuous self cooled rating of the
transformer by 33 1/3% for units rated 3750 kVA and below and 25% for units 3751 kVA and
larger. The FA rating increase shall be possible with forced cooling without exceeding the
specified maximum temperature rise. The forced air cooling shall be regulated automatically by
sensors placed in the low voltage winding’s air ducts. Forced air cooling shall include: three
phase electronic digital temperature monitor, fans, control wiring, control panel with test
switch, indicating lights, alarm and alarm silencing switch.
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Optional Overload Capabilities
When 80°C and 115°C winding temperature rise are specified, they can be designed with
inherent overload capabilities. An 80°C rise unit would be capable of continuous operation at
33% above nameplate rating and a 115°C rise unit would be capable of continuous operation at
15% above nameplate rating. This overload capability would be achieved on the AA and FA
rating and is accomplished by allowing the transformers’ maximum rise to be 150°C. Customer
specification must define the high capacity overloads.
Test
After completion, each transformer shall undergo the following routine production tests per
ANSI C57.12.01 and ANSI C57.12.91. Testing shall be accomplished using calibrated test
equipment, which have recorded accuracy traceable to National Institute of Standards
Technologies (NIST).
Accessories
Standard transformer accessories shall include:
• Diagrammatic instruction nameplate
• Provisions for lifting and jacking
• Removable case panel for access to HV taps
• Stainless steel ground pads
• Line voltage adjustment taps
Documentation
When requested, manufacturer shall provide copies of following documents to buyer for review
• A certified test report containing minimum information per IEEE C57.12.91
• Installation, maintenance, and operating instructions
• Outline Drawing
• Connection Diagram
• Nameplate Drawings
• Spare parts list
• Applicable wiring diagrams
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Medium Voltage Transformer Parts
Winding
Barriers
Leads
Coil Supports Core Clamps
Coils
Busbars
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Glossary of terms
Air Cooled: A transformer which uses air as the cooling medium. This may be natural draft
cooling by convection or forced air with the use of fans aka dry type transformer
FA: An air-cooled transformer with additional fans for increased air flow
FFA: The transformer has provisions so that fans may be added later.
BIL: Basic Insulation Level is a measure of the ability of the insulation system to withstand
surges
Core Loss: Losses caused by a magnetization of the core and its resistance to magnetic flux.
Delta: A standard three-phase connection in which each phase winding is connected in series to
form a closed loop.
Delta-Wye: The term used when indicating a method of connection for both primary and
secondary windings of a three-phase transformer bank.
Dielectric Tests: A series of tests conducted at much higher than rated nameplate voltage to
determine the effectiveness of insulating materials and electrical clearances.
Distribution Transformer: Any transformer rated between 3 and 500 KVA, inclusive with a
primary voltage of 601 volts or greater.
Electrostatic Shield: A grounded conductor sheet placed between the primary and secondary
winding to greatly reduce or eliminate line to line or line to ground noise. It is often referred to
as a Faraday shield.
Flexible Connector: A pliable conductor designed to compensate for thermal expansion and
contraction or reduce the transmission of objectionable noise.
Impedance: The vector sum of resistance and reactance, which limits the current flow in an AC
circuit. Impedance is identified in percentage and is used to determine the interrupting capacity
of circuit breakers, which protect the primary circuit.
Tap: A connection provided in a transformer winding which has the effect of changing the
nominal voltage ratio of the transformer. The taps are usually placed on the high voltage
winding to correct for high or low voltage conditions found on the low voltage output side. Taps
are expressed as either full capacity above nominal (FCAN) or full capacity below nominal
(FCBN).
CU/AL: the commonly accepted abbreviation for either Copper or Aluminum
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MGM TRANSFORMER COMPANY 5701 SMITHWAY STREET•••• CITY OF COMMERCE, CALIF. 90040
(323) 726-0888 •••• FAX (323) 726-8224
DRY TAKE OFF SHEET
Your Name Company
Phone # Email
Qty Enclosure Type Phase
KV Conductor Hz
Hv kV BIL
Lv kV BIL
Temp Rise 150°C 115°°°°C 80°°°°C
K Factor K-4 K-9 K-13 K-20 K-30
Taps DOE 2016 Efficiency
Options/ Accessories (this portion is not required)
Fan & Temperature Monitor
High Voltage Equipment
Low Voltage Equipment
Arresters
Drive Isolation (SCR Duty) Electro-static shields
Marine Duty Vaccum Pressure Impregnation
ABS Strip Heaters
Additional
Notes &
Comments
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